Get average of values over a period of time - mongodb

Question

I have the following collection:
{
"_id" : ObjectId("58503934034b512b419a6eab"),
"website" : "https://www.google.com",
"name" : "Google",
"keywords" : [
"Search",
"Websites",
],
"tracking" : [
{
"_id" : ObjectId("5874aa1df63258286528598d"),
"position" : 0,
"created_at" : ISODate("2017-01-1T09:32:13.831Z"),
"real_url" : "https://www.google.com",
"keyword" : "Search"
},
{
"_id" : ObjectId("5874aa1ff63258286528598e"),
"keyword" : "Page",
"real_url" : "https://www.google.com",
"created_at" : ISODate("2017-01-1T09:32:15.832Z"),
"found_url" : "https://google.com/",
"position" : 3
},
{
"_id" : ObjectId("5874aa21f63258286528598f"),
"keyword" : "Search",
"real_url" : "https://www.foamymedia.com",
"created_at" : ISODate("2017-01-2T09:32:17.017Z"),
"found_url" : "https://google.com/",
"position" : 2
},
{
"_id" : ObjectId("5874aa21f63258286528532f"),
"keyword" : "Search",
"real_url" : "https://www.google.com",
"created_at" : ISODate("2017-01-2T09:32:17.017Z"),
"found_url" : "https://google.com/",
"position" : 1
},
]
}
What I want to do is group all of the keywords together and calculate the average for that particular day, over a certain period.
So let's say for example:
Between: 2017-01-01 to 2017-01-31 the following keywords was tracked:
2017-01-01:
'Seach' => 1,
'Page' => 3,
Average = 2
2017-01-02:
'Search' => 4,
'Page' => 6,
Average = 5
....
So in the end result, I would be finished with (in this case):
{
"_id" : ObjectId("5874dccb9cd90425e41b7c54"),
"website" : "www.google.com",
"averages" : [
"2",
"5"
]
}

Answer 1

You can try something like this.
$unwind the tracking array followed by $sort on tracking.keyword and tracking.created_at.$group by day to get average for day across all categories. Final $group to push all the day's average values into array for a website.
db.website.aggregate([{
$match: {
"_id": ObjectId("58503934034b512b419a6eab")
}
}, {
$lookup: {
from: "seo_tracking",
localField: "website",
foreignField: "real_url",
as: "tracking"
}
}, {
$unwind: "$tracking"
}, {
$sort: {
"tracking.keyword": 1,
"tracking.created_at": -1
}
}, {
$group: {
_id: {
$dayOfMonth: "$tracking.created_at"
},
"website": {
$first: "$website"
},
"website_id": {
$first: "$_id"
},
"averageByDay": {
$avg: "$tracking.position"
}
}
}, {
$group: {
"_id": "$website_id",
"website": {
$first: "$website"
},
"average": {
$push: "$averageByDay"
}
}
}]);